Gear production



' teeth is indicative of Patented July 7, 1942 UNITED STATES PATENTOFFICE GEAR PRODUCTION Victor Fabian, Hamburg, Germany No Drawing.Application August 28, 1939, Serial No. 292,241. In Germany April 25,1935 1 Claim.

The present invention relates to the production of gears of an excellenthardness.

It has been proposed in the past to produce gears by case-hardening, lowcarbon, unalloyed or alloyed, steels containing a substantial amount ofchromium, nickel or molybdenum. The carbon content of such steelsusually varies between ,10 and .20%. This proposal was carried intoeffect by cementing" or carburizing the work pieces and subsequentlyhardening the same.

Preferably an annealing or hardening step was interposed. This procedureis objectionable not only because case-hardening is cumbersome inpractice but also because of the time-consuming nature thereof.

A further method sugg'estedby the art involved the bringing of the teethflanks of the gears only up to a certain depth to-the hardeningtemperature and then quenching; The adoption of this method has beennegatived because it is exceedingly troublesome to effect when dealingwith mass production. Moreover in all instances where a gear with aparticularly high hardness was desired it was necessary to resort to theuse a of alloyed steels. Because of the cost of the alloying metals,their utilization in the amounts required caused a material increase inthe expense oi the process.

I have now found that it is possible to avoid the objections inherent inthe prior art procedures and produce highly hardened gears withoutresort to the use of large amounts of the aboveexpensive alloyingmetalsby-selecting for the gears a steel containing from .5 to .l%,preferablyOIl to 0.8%, of carbon and hardening the gears whilecorrelating the temperature of treatment with certain factors pertainingto the steel and gear selected" for use.

Generally stated myprocess involves heating the gears to a hardeningtemperature above that usual for the steel selected for the gears, the

steel having for gears with an increasing tooth modulus, a decreasingcritical cooling speed, and quenching the gears in a bath, thetemperature of which lies only a little above, say about 20 C.,

r The factors with which I correlate the hardening temperature are themartensitic transformation point of the steel in question. As previouslynoted the steels should contain from .5 to 1% carbon. They may containother elements such as manganese, silicon, chromium, nickelor copper,but in such cases they will be weakly alloyed, the amounts of suchelements not exceeding the limits subsequently given. The temperature towhich the gears are heated is from 10 to 40 C. in excess of the usualhardening temperature. Thus it is known that for a steel containing from.7 to .8% carbon, the hardening temperature when the steel is to bewater-quenched, should be about 780 C.. If such a steel be used to formgears to be hardened by my method the most advantageous hardeningtemperature would be about 800 C. The particular temperature within thestated range will vary depending not only on the steel composition butalso as previously noted on the tooth modulus and the over all size ofthe work piece. However, it is comparatively simple when these factorshavebeen iixed to select the temperature producing optimum results.

The correlation of the tooth modulus of the.

steel with the "critical cooling speed thereof and the size of the workpieces is of importance for the reason that with'increasing tooththickness it is preferable to use a steel which is hardened through to agreater extent, that is a steel with a smaller critical cooling speed.The adoption of this measure is founded on the larger amount of heatwhich must be removed from the work piece.

The small critical cooling speed of the steel used may be achievedaccording to the general practice of adding the usual small amounts ofsilicon and manganese, i. e. from about .1 to

Iwishto' about .7 with steels containing from .5 to 1% 01' carbon, or bythe addition of small amounts of such metals as chromium, nickel andcopper,

that is amounts up to 0.5%.

I observed from my experiments that with steel of a certain manganesecontent, 1. e., .1%,

a through-hardening of the gears resulted at a content as said modulusvaries. Thus to obtafii satisfactory hardening as said modulus variesfrom 1 to '7, the manganese content must progressively shift from .1 to.'7% i. e., with a modulus of 2, the manganese will amount to 2%, with amodulus of 5, the manganese will amount to .5%, and so on.

The tooth modulus also governs to a large ex tent the duration of thequenching operation, although here too the over all size of the workpiece must be considered. It is therefore preferable to establish theperiod of quenching for each tooth modulus of each work piece.

The following example will serve to illustrate my invention although itis to be understood that my invention is not restricted thereto.

Example A gear, formed of an unalloyed carbon steel, containing .7 to.8% carbon and .1% manganese, and having a tooth modulus of 1 was heatedabove its transformation point to 800 C. and quenched in a salt bathcomprising barium chloride maintained at a temperature of about 200 ing,for gears with a tooth modulus M ranging from 1 to 7, such tooth modulusof the gears with the critical cooling speed of the steels of the gears,so that for gears with a tooth modulus increasing within'said range, thesteels thereof have a decreased critical cooling speed, heatingthe'gears to a temperature above the critical hardening temperature ofsaid steels and quenching the gears in a bath, the temperature of whichis maintained slightly above the point of martensitic formation of saidsteels, the rate of quenching being higher the higher the criticalcooling speed and vice versa,

C M equals 0 being the circumference of the gear and N the number ofteeth.

VICTOR FABIAN.

